We previously demonstrated that beta-D-xylopyranosyl-(1-->3)-beta-D-glucuronopyranosyl
echinocystic acid (
codonoposide 1c), a biologically active compound isolated from the roots of Codonopsis lanceolata, is cytotoxic to
cancer cells. In the present study, we investigated the effects of
codonoposide 1c on the induction of apoptosis, and its putative action pathway in HL-60 human promyelocytic
leukemia cells.
Codonoposide 1c-treated HL-60 cells displayed several features of apoptosis, including DNA fragmentation, formation of
DNA ladders by
agarose gel electrophoresis, and externalization of
annexin-V targeted
phosphatidylserine (PS) residues. We observed that
codonoposide 1c caused activation of
caspase-8,
caspase-9, and
caspase-3. A broad
caspase inhibitor (
z-VAD-fmk),
caspase-8 inhibitor (
z-IETD-fmk), and
caspase-3 inhibitor (
z-DEVD-fmk) almost completely suppressed
codonoposide 1c-induced DNA fragmentation. We further found that
codonoposide 1c induces mitochondrial translocation of Bid from cytosol, reduction of cytosolic Bax, and
cytochrome c release from mitochondria. Interestingly,
codonoposide 1c also triggered the mitochondrial release of Smac/DIABLO (second mitochondria-derived activator of
caspases/direct inhibitor of apoptosis-
binding protein with a low isoelectric point) into cytosol, and a reduction in
X-linked inhibitor of apoptosis protein (XIAP). Taken together, our data indicate that
codonoposide 1c is a potent inducer of apoptosis and facilates its activity via Bid cleavage and translocation to mitochondria, Bax reduction in cytosol, release of
cytochrome c and Smac/DIABLO into the cytosol, and subsequently
caspase activation, providing a potential mechanism for the cytotoxic activity of
codonoposide 1c.